A spatial light modulator (SLM) is a device that spatially varies or modulates a beam of light reflected therefrom or transmitted therethrough. An SLM is typically used in conjunction with a coherent light source, such as a laser, to modulate an intensity of the beam, a phase of the beam or both simultaneously. Spatial light modulators are widely used and growing in popularity for a number of different applications including printing, imaging or display and photolithography systems used in semiconductor fabrication.
Spatial light modulators can be classified as either binary (on-off) or analog (gray-scale). The Digital Mirror Device (DMD) is an example of a reflective binary spatial light modulator. Light from a DMD pixel is either transmitted or blocked depending on which of two stable positions the micro-mirror assumes. Analog spatial light modulators are exemplified by the Grating Light Valve (GLV), the Planar Light Valve (PLV™), both of which are available from Silicon Light Machines Corporation of Sunnyvale, Calif., and by liquid crystal (LC) light modulators. In these devices, the intensity of transmitted light can be continuously varied between bright and dark states depending on the strength of the input drive voltage.
Typically, analog spatial light modulators are controlled by digital input codes in conjunction with a digital-to-analog converter (DAC). The resolution of the gray-scale is determined by the bit-depth of the DAC. For example, an 8-bit DAC provides 28=256 grey-levels and a 10-bit DAC provides 210=1024 gray levels. There can be a dedicated DAC per pixel, or a single DAC can be shared among pixels via time-multiplexing.
Schematics of intensity versus a digital-to-analog converter (DAC) response for a binary spatial light modulator and a conventional analog spatial light modulator are shown in FIGS. 1A and 1B respectively. Due to their analog nature, analog SLM's typically require much higher data transmission rates relative to binary spatial light modulators. For example, consider a 1 k×2 k pixel binary SLM operating at a 1 kHz frame rate. The control code driving each mirror is simply a 1 or a 0—only a single bit is needed per pixel. In this case the data rate is: (1 bit/pixel)×(1000×2000 pixels/frame)*(1000 frames/s)=2 Giga-bits/s. FIG. 1B illustrates DAC response in the same pixel array in a 10-bit analog SLM. In this case, the data rate is: (10 bits/pixel)×(1000×2000 pixels/frame)*(1000 frames/s)=20 Giga-bits/s. Not surprisingly, the bit depth associated with analog spatial light modulator directly impacts the net data rate to the SLM: at the same frame rate, the 10-bit analog SLM requires 10× higher data rate relative to the binary SLM.
Accordingly, there is a need for SLMs and a method for operating the same for efficient data transmission.